Help: Read in data from the serial com in real time.

5 posts
by cybersmile » Thu Dec 20, 2012 11:06 am
Hello community, I have myself a pi and a serial connection to a device, that is outputting data to the pi.

When I load up minicom I can see the data on the port coming up just fine so my wiring and 3v3 is all correct.

What I am trying to do with this data is store it in a txt or log file in real time and constantly. So any data coming in is recorded in the text file in real time.
The txt file will be accessed by a PHP, or C script to get the data into the program and outputted to a display.

I want the program to run in a loop, and the data reading to run in a loop. How can I do this.

I run the shell command.
Code: Select all
sudo cat /dev/ttyAMA0 > captured.txt
yet my text file updates randomly and sometimes doesn't update.
Can anyone help me use the shell to record the data to the text file whenever it comes in.
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by cybersmile » Thu Dec 20, 2012 1:26 pm
I have found I can do this with minicom
Code: Select all
sudo minicom -C data.txt
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Joined: Thu Dec 20, 2012 10:44 am
by rurwin » Thu Dec 20, 2012 1:33 pm
The problem is probably that the data will be buffered in RAM for some indeterminate period before being written to the file. Because there is no human in the link, Linux assumes it can take its time.
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by lindymood » Wed Feb 06, 2013 7:11 pm
I have messed with minicom but found that it limited certain charcters. I wanted to capture all characters including PCL from a printer port.

Github provided a version of that receives the serial port data and redirects it to a specific TCP port such as an Ethernet printer. ...

This was the "Holy Grail" for what I needed to do. I modified it to write the same data to a text file and to ignore the Ethernet redirect if there is no connection.

My raspberry pi, with the addition of a serial RS232 DB9 level shifter is now a fantastic device server with serial text capture ability. I have also replaced older serial printers with any printer that uses the raw telnet port 9100 protocol. It is reliable and captures everything.

Below is my version of the Python code. Pyserial is needed which can be easily installed. Just modify the logfile path and set the arguments for the Ethernet path and port:

EX: ./ -H -P 9100

I want to share this because of the help and support of others that made this possible. Have fun!

Code: Select all
#!/usr/bin/env python

# based on from pyserial

""" Added logging and ping feature. The additions write the data stream to a text file
and tests the communication to the printer port. If communication is lost, the data transfer to
TCP is suspended. The communication test interval is 1 minute when the serial port is idle.

USAGE: [options]
Simple Serial to Network (TCP/IP) redirector.

This redirector waits for data from the serial port, then connects
to the remote host/port and relays data back and forth.  If either
the COM port or the socket is closed, it restarts and waits for a
new connection on the COM port.

  -p, --port=PORT   serial port, a number, defualt = 0 or a device name
  -b, --baud=BAUD   baudrate, default 9600
  -r, --rtscts      enable RTS/CTS flow control (default off)
  -x, --xonxoff     enable software flow control (default off)
  -H, --iphost      Remote TCP/IP host (default
  -P, --ipport      Remote TCP/IP port (default 9000)

Note: Only one connection at once is supported. If the connection is terminaed
it waits for the next connect.

import sys, os, threading, getopt, socket, subprocess, datetime

    import serial
    print "Running serial_tcp_redirect requries pyserial"
    print "available at"

except NameError:
    True = 1
    False = 0

class pingCommunication():
    def __init__(self, ipToPing):
        self.ipToPing = ipToPing
        self.pingQuantity = "1"
    def pingProcess(self):
        pingTest = "ping -c "+ self.pingQuantity + ' ' + self.ipToPing
        #print pingTest -DL- Unremark for testing
        process = subprocess.Popen(pingTest, shell=True, stdout=subprocess.PIPE)
        returnCodeTotal = process.returncode
        return returnCodeTotal

class SerialRedirector:
    def __init__(self, ping_addr, tcp_addr, com_port, baudrate=9600, rtscts=False,
                 xonxoff=False, timeout=60):
      # print "PRINTER IP ADDRESS IS %r" % (ping_addr) = ping_addr
   self.addr = tcp_addr
        self.socket = None
        self.thread_write = None
        self.alive = False
        # create the serial connection
        ser = serial.Serial()
        ser.port    = com_port
        ser.baudrate = baudrate
        ser.rtscts  = rtscts
        ser.xonxoff = xonxoff
        ser.timeout = timeout     #required so that the reader thread can exit
        except serial.SerialException, e:
            print "Could not open serial port %s: %s" % (ser.portstr, e)
        self.serial = ser

    def go(self):
        """wait for incoming com data, then redirect
            to the tcp port"""
        self.alive = True
    def socketStart(self):
        print "CONNECTING TO IDE AT %r" % self.addr
        # create the socket connection
            self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            self.socket.connect((self.addr[0], self.addr[1]))
        except socket.error, details:
            self.socket = None
        # start redirecting from serial to tcpip
        self.thread_write = threading.Thread(target=self.writer)
    def reader(self):
        """loop forever and copy serial->socket"""
        print "Serial To TCP Application Started Using Port %s %s\n\nTCP/Printer IP Adress: %s\n\n" % (self.serial.portstr, str(,
        data = None
   comOK = 2
   data_on = 2
        while not data:
#       print comOK # -DL- remove remark for testing
            comunicate = pingCommunication(
            ignoreTCP = comunicate.pingProcess()
       if ignoreTCP == 0:
      if not comOK == 1:
              print "PRINTER CONNECTED  %s %s\n\n" %(self.addr, str(
      comOK = 1
      if not comOK == 0:
          print "PRINTER DISCONNECTED %s %s\n\n" %(self.addr,  str(
      comOK = 0
            data =              #read one, blocking
            n = self.serial.inWaiting()             #look if there is more
#        print "Received serial data on %s" % self.serial.portstr
#        print "data [%r]" %data -DL- ????
        while self.alive:
                if n:
                    data = data +   #and get as much as possible
                if data:
          logfile = open("/var/www/active_log.txt","a")
                    #print ("%s" %data, end="")-DL- Removed for final testing
                    if not self.socket and ignoreTCP == 0:
          if comOK == 1:
                       self.socket.sendall(data)           #send it over TCP
          if not data_on == 1:
         print "DATA RECEIVED  " + str(
          data_on = 1
               comunicate = pingCommunication(
               ignoreTCP = comunicate.pingProcess()
               if ignoreTCP == 0:
                   if not comOK == 1:
                       print "PRINTER CONNECTED %s %s\n\n" %(self.addr,  str(
                     comOK = 1
                   if not comOK == 0:
                           print "PRINTER DISCONNECTED %s %s\n\n" %(self.addr, str(
                   comOK = 0
          if data_on == 1:
                        print "SERIAL PORT IDLE  %s\n\n" % str(
          data_on = 0
                data =              #read one, blocking
                n = self.serial.inWaiting()             #look if there is more
            except socket.error, msg:
                print msg
                #probably got disconnected
        self.alive = False
        if self.thread_write:
    def writer(self):
        """loop forever and copy socket->serial"""
        while self.alive:
                data = self.socket.recv(1024)
                if not data:
                #print "socket data [%r]" % data  -DL- removed for final testing
                self.serial.write(data)                 #get a bunch of bytes and send them
            except socket.error, msg:
                print msg
                #probably got disconnected
        self.alive = False
        # close the socket
        except socket.error, details:
            pass #we quiting, dont care about the error
        self.socket = None

    def stop(self):
        """Stop copying"""
        if self.alive:
            self.alive = False

if __name__ == '__main__':
    #parse command line options
        opts, args = getopt.getopt(sys.argv[1:],
                ["help", "port=", "baud=", "rtscts", "xonxoff", "ipport=", "iphost="])
    except getopt.GetoptError:
        # print help information and exit:
        print >>sys.stderr, __doc__
    ser_port = '/dev/ttyAMA0'
    baudrate = 9600
    rtscts = False
    xonxoff = False
    iphost = ''
    ipport = 9100
    for o, a in opts:
        if o in ("-h", "--help"):   #help text
        elif o in ("-p", "--port"):   #specified port
                ser_port = int(a)
            except ValueError:
                ser_port = a
        elif o in ("-b", "--baud"):   #specified baudrate
                baudrate = int(a)
            except ValueError:
                raise ValueError, "Baudrate must be a integer number"
        elif o in ("-r", "--rtscts"):
            rtscts = True
        elif o in ("-x", "--xonxoff"):
            xonxoff = True
        elif o in ("-H", "--iphost"):
            iphost = a
        elif o in ("-P", "--ipport"):
                ipport = int(a)
            except ValueError:
                raise ValueError, "Local port must be an integer number"

    print "\n---Serial to TCP/IP redirector ---\nVersion 0 Jan-10-2013 By -DL-\n\n"

    while 1:
            #enter console->serial loop
            r = SerialRedirector(iphost,[iphost, ipport],
                                 ser_port, baudrate, rtscts, xonxoff)
        except socket.error, msg:
            print msg

    print "\n--- exit ---"

Posts: 9
Joined: Wed Feb 06, 2013 6:43 pm
by lindymood » Wed Feb 06, 2013 8:40 pm
I forgot to add that the text file can also be printed to PDF using Ghostscript PCL2PDF. This is why I needed the PCL characters that Minicom ignored.

I am new to the forum so I must get used to the tools.
Posts: 9
Joined: Wed Feb 06, 2013 6:43 pm